fix #H260 - escaping lava let you stay there indefinitely

<email deleted>, escaping from being stuck
by lava via jumping--or simply walking--got you out of the lava while being
at the same location.  You could then stay there for as long as you liked
without falling back in.  This makes a lava and water check on turns where
time passes but hero hasn't moved, performing a subset of spoteffects().
I think the water case only matters when using wizard mode to wish for a
pool or moat, which gets created at hero's feet without making him fall in
(unlike wishing for lava, where hero does immediately fall in).

include/extern.h

@@ -777,6 +777,7 @@ E boolean FDECL(test_move, (int, int, int, int, int));
 E void NDECL(domove);
 E void NDECL(invocation_message);
 E void FDECL(spoteffects, (BOOLEAN_P));
+E void NDECL(stayeffects);
 E char *FDECL(in_rooms, (XCHAR_P,XCHAR_P,int));
 E boolean FDECL(in_town, (int,int));
 E void FDECL(check_special_room, (BOOLEAN_P));